The increasing possibilities of radioiodine exposure from various sources, i.e. fallout from nuclear weapon tests, accidental release from nuclear energy institutions or the wide spread use of radioiodine in the medical field, emphasize a need to develop the prophylactic measures for radioiodine contamination of humans especially newborn infants, pregnant mothers and fetus.
As a part of the study, a preliminary experment was carried out on the distribution of I-131 in maternal and fetal tissues at the various intervals following oral or intratracheal administration of I-131 into pregnant mice of 18 days of gestation.
1. Thyroidal I-131 content of both mother and fetus reached a peak value at about 24 hours after the administration.
2. The concentration of I-131 in whole fetus reached a maxmum at 2 hours following the administration, while the concentration in maternal body decreased continously.
3. The fetal I-131 concentration was found to be higher than the maternal concentration during the period of observation from 1 hour to 48 hours after the administration, and in the ratio of fetus-to-mother a maximum value of about 3 was obtained at 2 hours after the administration.
4. Among the various tissues of mother, placenta, uterus and mammary glands seemed to concentrate I-131 and the highest values were observed at 2 hours after the administration.
5. Significant differences of the distribution of I-131 was not observed between the oral and the tracheal routes of administration in pregnant mice, while in rats, the I-131 retention for intratracheal administration was found to be higher than the level for ingestion.
6. The 24 hour thyroidal uptake and whole body retention of I-131 in pregnant and fetal mice was observed to be the highest in summer and the lowest in autumn.